(a) Field of the Invention
The present invention relates to a plasticizer of polyvinylchloride(PVC, hereinafter) and flexible PVC blend, and more particularly, aliphatic polyester having highly branched structure and flexible PVC blend containing the same, allowing to overcome problems such as the disturbance of endocrine system of human body and the destruction of ecosystem due to the efflux of plasticizer and having superior compatibility with polyvinylchloride and superior efficiency to plasticize, thereby giving polyvinylchloride sufficient flexibility.
(b) Description of the Related Art
PVC is a typical polymer widely used for manufacturing plumbing pipes, food packing material, goods for infants such as baby bottles and toys, fiber for textile, articles for interior decoration, receptacles for blood storage, etc. Such PVC has rigid property since the same has peculiar hierarchy structure inside molecule and microcrystallite functioning as physical crosslinks to allow the molecular movement to be restricted. Accordingly, flexibility should be given through the plasticization process to use PVC for the products requiring flexibility such as film for packing food. Flexible PVC is generally manufactured by adding plasticizer to PVC. Adding plasticizer improves the molecular movement of PVC to give flexibility to PVC.
There may be mentioned as plasticizer widely used for manufacturing flexible PVC, di[2-ethylhexyl]phthalate(DOP, hereinafter), dibutyl phthalate, dibenzyl phthalate, di[2-ethylhexyl] adipate, etc. They are all liquid plasticizer having low molecular weight. The reasons why such low molecular weight plasticizer has superior plasticization efficiency are as follows.
First, low molecular weight plasticizer accelerates the chain-end motion by increasing the number of end-group in a fixed volume to improve the molecular movement of PVC.
Second, low molecular weight plasticizer accelerates the main-chain motion by widening distance between the chains of PVC and deteriorating the interactivity therebetween to improve the molecular movement of PVC.
Third, the molecular movement of compound of PVC and plasticizer is improved since the chain of low molecular weight plasticizer is short to have good molecular movement.
By reason as described above, low molecular weight plasticizer is very useful for manufacturing flexible PVC. However, since low molecular weight plasticizer is liquid material, the same tends to volatilize into the air or to transfer to the outside through the contact with liquid or solid substance. When the plasticizer flowing out like this flows into the human""s body, the animal, or the plant, the same strikes a fatal blow by hindering the normal activity of the endocrine system, which is directly concerned with the life activity or stirring the abnormal reaction. For this reason, the related organizations and the environmental protection organizations of all the countries of the world specifies the most of low molecular weight plasticizers for PVC as hindrance material to the endocrine system(also known as environmental hormone) and restricts or permits only temporarily the use of them.
Accordingly, the researches to develop plasticizer for PVC to substitute the low molecular weight plasticizer and not to flow out are progressed. Such researches are mostly about plasticizer formed of linear polymer, which does not flow out from the PVC goods.
For example, in U.S. Pat. No. 5,385,974, there is disclosed PVC plasticizer formed of vinyl acetate, ethylene oxide, and caprolactone copolymer having 1,500xcx9c1,000,000 of molecular weight. When such linear polymer is used as plasticizer of PVC, the problem of efflux of plasticizer as in case of the low molecular weight plasticizer does not occur. However, since the number of end-group of linear polymer is small, the improvement of the molecular movement due to the accelaration of chain-end motion is impossible. In addition, since chain entanglement occurs because of the property of linear polymer, the molecular movement is restrained. Accordingly, the plasticization efficiency is not good enough and therefore, the required flexibility is not sufficiently given to PVC.
It is an object of the present invention is to overcome the above-mentioned problems and to provide aliphatic polyester compound for PVC plasticizer, having highly branched structure, allowing to overcome problems such as the disturbance of endocrine system and the destruction of ecosystem due to the efflux of plasticizer and having superior compatibility with PVC and superior efficiency to plasticize, thereby giving PVC sufficient flexibility.
To achieve the above object, the present invention provides aliphatic polyester compound having highly branched structure formed by the self-condensation polymerization of xcex1-carboxy-xcfx89-2,2-[bis(hydroxymethyl)propanoate]polyester indicated in following chemical formula 1. 
In the above chemical formula 1, m is an integer of 3 to 15 and the degree of polymerization n is an integer of 5 to 100.
In addition, to achieve the above object, the present invention provides aliphatic polyester compound having highly branched structure formed by the self-condensation polymerization of 2,2-bis(xcfx89-hydroxy polyestermethyl)propionic acid indicated in following chemical formula 2. 
In the above chemical formula 2, m is an integer of 3 to 15 and the degree of polymerization n is an integer of 5 to 100.
Aliphatic polyester compound having highly branched structure according to the present invention is formed by the self-condensation polymerization of monomer having one carboxy functional group and two hydroxy functional groups. Aliphatic polyester compound having highly branched structure according to the present invention has superior compatibility with PVC, does not flow out, and is not restrained in the molecular movement since the same has a large number of branches, so little chain entanglement occurs in comparison with linear polymer. In addition, since the inventive compound has a large number of terminal groups, the same has superior molecular movement. Further, since aliphatic polyester compound having highly branched structure according to the present invention has a three-dimensional semi-globular cubic molecular structure, the chain entanglement of PVC chain is prevented on blending with PVC, thereby improving the molecular movement of PVC. Accordingly, aliphatic polyester compound having highly branched structure according to the present invention gives PVC sufficient flexibility without flowing out.
Number average molecular weight of aliphatic polyester compound having highly branched structure according to the present invention is preferably 1,000xcx9c1,000,000.
It is another object of the present invention to provide flexible PVC blend harmless to humans, that can be used for manufacturing food and medical supplies packing material, goods for infants such as baby bottles and toys, receptacles for blood storage, etc.
To achieve another object, the present invention provides flexible PVC blend formed of 5xcx9c50 weight % of the aliphatic polyester compound having highly branched structure and 95xcx9c50 weight % of PVC.